Processing device

ABSTRACT

In a processing apparatus for performing a specified process on a target object at a predetermined process pressure, the apparatus includes an evacuable processing chamber having a gas exhaust port formed in a bottom portion thereof; a mounting table provided within the processing chamber for holding the target object; a pressure control valve connected to the gas exhaust port, the pressure control valve including a slide-type valve body for changing an area of an opening region of a valve port; and a gas exhaust system connected to the pressure control valve. The pressure control valve is eccentrically arranged such that a center axis of the mounting table lies within an opening region of the pressure control valve formed over a practical use region of a valve opening degree of the pressure control valve.

FIELD OF THE INVENTION

The present invention relates to a single wafer plasma processingapparatus for use in performing various kinds of processes, such asplasma processing, film-forming and etching, on semiconductor wafers orthe like sheet by sheet.

BACKGROUND OF THE INVENTION

In order to manufacture semiconductor products such as a semiconductorintegrated circuit and the like, it is general that a semiconductorwafer is repeatedly subjected to various kinds of processes, includingfilm-forming, etching, oxidizing and diffusing, ashing and reforming. Asthe semiconductor products become highly dense and miniaturized, thevarious kinds of processes need to be performed with high in-planeuniformity in view of the improvement of a product yield rate.

In this regard, a plasma processing apparatus will be described as anexample of the conventional single wafer plasma processing apparatus.Plasma processing apparatuses are disclosed in, e.g., Japanese PatentLaid-open Publication Nos. H3-191073, H5-343334, H9-181052 and2002-311892. FIG. 11 is a schematic configuration view showing aconventional plasma processing apparatus.

Referring to FIG. 11, the plasma processing apparatus 2 includes anevacuable processing chamber 4 and a mounting table 6, provided withinthe processing chamber 4, for mounting a semiconductor wafer W thereon.The mounting table 6 is supported by an “L”-like support arm 7 extendingfrom a sidewall of the processing chamber 4. A disk-like ceiling plate 8that transmits microwaves is air-tightly provided in a ceiling portionof the processing chamber 4 in a facing relationship with the mountingtable 6. The ceiling plate 8 is made of aluminum nitride, quartz or thelike. A gas nozzle 9 for introducing a specified gas into the processingchamber 4 is formed in the sidewall of the processing chamber 4.

On an upper surface of the ceiling plate 8, there are installed adisk-like planar antenna member 10 having a thickness of about severalmillimeters and a retardation member 12 for shortening the wavelength ofmicrowaves in a radial direction of the planar antenna member 10. Theretardation member 12 is made of, e.g., a dielectric material. Aplurality of microwave irradiation holes, e.g., elongated through-holes,is formed in the planar antenna member 10. The microwave irradiationholes 14 are usually arranged in a concentric pattern or a spiralpattern. A central conductor 18 of a coaxial waveguide tube 16 isconnected to a central portion of the planar antenna member 10 so thatthe microwaves of, e.g., 2.45 GHz, generated in a microwave generator 20is converted to a specified vibration mode by means of a mode transducer22 and then sent to the planar antenna member 31. While propagatingradially of the planar antenna member 10, the microwaves are irradiatedthrough the microwave irradiation holes 14 formed in the planar antennamember 1. Then, the microwaves are transmitted through the ceiling plate8 and introduced into the processing chamber 4, whereby the microwavesgenerate plasma in a processing space S within the processing chamber 4.

A gas exhaust port 24 is formed in a central region of a bottom portion4A of the processing chamber 4. A pressure control valve 26 is attachedto the gas exhaust port 24. The pressure within the processing chamber 4is regulated by controlling the opening degree of the pressure controlvalve 26 and consequently changing the area of an aperture of a valveport 28. The pressure control valve 26 is of, e.g., a gate valve. Theopening degree, i.e., the aperture area, of the pressure control valve26 is controlled by slidingly moving a valve body 30 in the directionindicated by arrow 31, e.g., in a horizontal direction. A turbomolecular pump 32 as a vacuum pump of a gas exhaust system is connectedto a gas outlet side of the pressure control valve 26 so that it canevacuate the processing chamber 4 into a vacuum state. With thisconfiguration, plasma is generated in the processing space S within theprocessing chamber 4 and a semiconductor wafer W is subjected to plasmaprocesses such as plasma etching, plasma film-forming and the like.

In order to increase the yield rate of products as mentioned above, theplasma processes need to be uniformly performed over a wafer plane. In ageneral single wafer processing apparatus as well as the plasmaprocessing apparatus noted above, the processing uniformity is heavilyaffected by a way of causing a gas to flow within the processing spaceS. To that end, the gas exhaust port 24 and the valve port 28 of thepressure control valve 26 are arranged in the central region of thebottom portion 4A of the processing chamber 4 while, for example, acenter axis of the mounting table 6 is in alignment with the center axisof the gas exhaust port 24 and the valve port 28. In this way, theambient gas within the processing space S is allowed to uniformly flowaround the mounting table 6 and then flow down toward the gas exhaustport 24 positioned below the mounting table 6.

With the arrangement of the pressure control valve 26 as set forthabove, if the valve opening degree is equal to 100%, the ambient gaswithin the processing space S flows down in a state that it is uniformlydistributed around the mounting table 6. However, if the valve openingdegree is small as is the case in an actual process, there occurs adeviation in the gas flow. In other words, when the afore-mentionedpressure control valve 26 is used for the purpose of pressure control,it is necessary to regulate the target control pressure as the processpressure with a good controllability with respect to a pressure rangearound the target control pressure. To this end, it is general that therange of the valve opening degree practically used in the process is setequal to about 5 to 40%. The practical use range of the valve openingdegree noted above is also recommended by control valve makers as adesirable use range.

Stating differently, if the processing apparatus is designed to controlthe process pressure with an excessively small valve opening degree oran excessively high valve opening degree, the change in gas exhaustconductance relative to the change in the valve opening degree is toosmall or too great to stably control the pressure. In view of this, theprocessing apparatus available in practice is as a whole designed toensure that the pressure range around the target control pressure can bestably controlled in a process by using the pressure control valve 26 ata valve opening degree of about 20%.

However, in case the valve opening degree of the pressure control valve26 is as small as 20%, the valve port 28 is mostly closed by the valvebody 30 as illustrated in FIG. 12, which is a plan view of the valveport 28. The opening region M (the hatched region in FIG. 12) throughwhich a gas actually passes has a shape of crescent. Therefore, theopening region M is positioned far away from the center axis 6A of themounting table 6.

This creates a deviation in the flow rate of a gas flowing down aroundthe mounting table 6 as indicated by an arrow 34 in FIG. 11. As aconsequence, it becomes impossible to uniformly exhaust the gas fromaround the mounting table 6. This poses a problem in that the in-planeuniformity is reduced when processing a wafer. This problem becomesconspicuous as the size of a gas exhaust port grows larger together withthe increase in the wafer size to 300 mm and the resultant increase inthe size of the processing chamber 4.

SUMMARY OF THE INVENTION

In view of the problems mentioned above and for the purpose ofeffectively solving the problems, it is an object of the presentinvention to provide a processing apparatus capable of exhausting anambient gas in a processing space in a state that the ambient gas isuniformly distributed around a mounting table when a valve openingdegree varies within a practical use region. This comes true byarranging a pressure control valve in a gas exhaust port eccentricallyfrom a center axis of the mounting table.

In accordance with an aspect of the present invention, there is provideda processing apparatus for performing a specified process on a targetobject at a predetermined process pressure, the apparatus including: anevacuable processing chamber having a gas exhaust port formed in abottom portion thereof; a mounting table provided within the processingchamber for holding the target object; a pressure control valveconnected to the gas exhaust port, the pressure control valve includinga slide-type valve body for changing an area of an opening region of avalve port; and a gas exhaust system connected to the pressure controlvalve, wherein the pressure control valve is eccentrically arranged suchthat a center axis of the mounting table lies within an opening regionof the pressure control valve formed over a practical use region of avalve opening degree of the pressure control valve.

In this way, the pressure control valve is eccentrically provided suchthat the center axis of the mounting table lies within the openingregion formed over the practical use region of the valve opening degreeof the pressure control valve. By arranging the pressure control valvein the gas exhaust port eccentrically from the center axis of themounting table, it is possible to exhaust the ambient gas in theprocessing space in a uniformly distributed state around the mountingtable when the pressure control valve is used in the practical useregion of the valve opening degree. This makes it possible to processthe target with increased in-plane uniformity.

In this case, for example, the gas exhaust port is formed eccentricallyrelative to the center axis of the mounting table.

Further, for example, the practical use region of the valve openingdegree is in a range of 5 to 40%.

Furthermore, for example, the center axis of the mounting table ispositioned on a movement trajectory of a gravity center of a planedefined by the opening region.

In addition, for example, the gas exhaust system includes a turbomolecular pump connected to the pressure control valve.

Moreover, for example, the valve body is rectilinearly slidable.

Further, for example, the valve body is curvilinearly and swingablyslidable.

Furthermore, for example, the mounting table is supported by a sidewallof the processing chamber through a support arm.

In addition, for example, the mounting table is supported on the bottomportion of the processing chamber through support legs.

The processing apparatus in accordance with the present inventionprovides the advantageous effects as follows.

The pressure control valve is eccentrically provided such that thecenter axis of the mounting table lies within the opening region formedover the practical use region of the valve opening degree of thepressure control valve. By arranging the pressure control valve in thegas exhaust port eccentrically from the center axis of the mountingtable, it is possible to exhaust the ambient gas in the processing spacein a uniformly distributed state around the mounting table when thepressure control valve is used in the practical use region of the valveopening degree. This makes it possible to process the target object withincreased in-plane uniformity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration view showing one example of a processingapparatus in accordance with the present invention.

FIGS. 2A to 2D are views explaining the change in a valve opening degreeof a pressure control valve.

FIG. 3 is a plan view illustrating one example of the movementtrajectory of a gravity center of the plane defined by an openingregion.

FIG. 4 is a schematic view illustrating the flow of an exhaust gas inthe processing apparatus of the present invention.

FIGS. 5A and 5B are graphs representing the relationship between a valveopening degree of a pressure control valve and a pressure within aprocessing chamber and the relationship between a valve opening degreeof a pressure control valve and an exhaust conductance.

FIG. 6 is a section view showing a modified example of the pressurecontrol valve.

FIGS. 7A to 7C are views explaining the change in a valve opening degreeof the pressure control valve shown in FIG. 6.

FIG. 8 is a plan view illustrating the movement trajectory of a gravitycenter of the plane defined by an opening region when a valve openingdegree is in the range of 5 to 40%.

FIG. 9 is a view showing a modified example of an attachment structureof a vacuum pump.

FIG. 10 is a view showing a modified example of an attachment structureof a mounting table.

FIG. 11 is a schematic configuration view showing a conventional generalprocessing apparatus.

FIG. 12 is a plan view illustrating a state that the valve openingdegree of a pressure control valve is about 20% in the conventionalprocessing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, one embodiment of a processing apparatus in accordance withthe present invention will be described with reference to theaccompanying drawings.

FIG. 1 is a configuration view showing one example of a processingapparatus in accordance with the present invention. FIGS. 2A to 2D areviews explaining the change in a valve opening degree of a pressurecontrol valve. FIG. 3 is a plan view illustrating one example of themovement trajectory of a gravity center of the plane defined by anopening region. FIG. 4 is a schematic view illustrating the flow of anexhaust gas in the processing apparatus of the present invention. FIGS.5A and 5B are graphs representing the relationship between the valveopening degree of the pressure control valve and a pressure within aprocessing chamber and the relationship between the valve opening degreeof the pressure control valve and an exhaust conductance. A plasmaprocessing apparatus will be described herein as an example of theprocessing apparatus.

As shown in the drawings, a plasma processing apparatus 40 as oneexample of the processing apparatus includes a processing chamber 42formed into a tubular shape as a whole. The processing chamber 42 has asidewall and a bottom wall, both of which are made of a conductingmaterial such as aluminum or the like. A hermetically sealed processingspace S is formed within the processing chamber 42 so that plasma can begenerated in the processing space S. The processing chamber 42 iselectrically grounded.

In the processing chamber 42, there is disposed a mounting table 44 formounting, e.g., a semiconductor wafer W as a target object to beprocessed on its upper surface. The mounting table 44 is formed into agenerally disk-like flat shape and is made of, e.g., alumite-treatedaluminum. The mounting table 44 is supported by the sidewall of theprocessing chamber 42 through an “L”-like curved support arm 46 made of,e.g., aluminum or the like.

A gate valve 48 is provided in the sidewall of the processing chamber 42and it is opened and closed when the semiconductor wafer W is loadedinto and unloaded out of the processing chamber 42. A gas exhaust port50 through which an ambient gas in the processing chamber 42 isexhausted is formed in a bottom portion 49 of the processing chamber 42.

The processing chamber 42 is opened at its ceiling portion. Amicrowave-transmitting ceiling plate 52 made of a ceramic material,e.g., Al₂O₃, or quartz is air-tightly installed in the ceiling portionof the processing chamber 42 through a seal member 54 such as an O-ringor the like. Taking a pressure resistance into account, the ceilingplate 52 is formed to have a thickness of, e.g., about 20 mm.

On an upper surface of the ceiling plate 52, there is provided a plasmagenerating unit 56 for generating plasma within the processing chamber42. Specifically, the plasma generating unit 56 includes a disk-likeplanar antenna member 58 provided on the upper surface of the ceilingplate 52. A retardation member 60 is arranged on the planar antennamember 58. The retardation member 60 has a high dielectric constant sothat it can shorten the wavelength of microwaves. The planar antennamember 58 serves as a bottom plate of a waveguide box 62 which is anelectrically-conductive hollow cylindrical container that covers theupper portion of the retardation member 60. The planar antenna member 58is provided in a facing relationship with the mounting table 44 in theprocessing chamber 42.

The peripheral portions of the waveguide box 62 and the planar antennamember 58 are all kept in electric conduction with the processingchamber 42. An outer tube 64A of a coaxial waveguide tube 64 isconnected to a central upper portion of the waveguide box 62. An innerconductor 61B of the coaxial waveguide tube 64 is connected to a centralregion of the planar antenna member 58 through a central through-hole ofthe retardation member 60. The coaxial waveguide tube 64 is connected toa microwave generator 70 having an output power of, e.g., 2.45 GHz, viaa mode transducer 66, a waveguide tube 68 and a matching box (not shown)with a matching function, so that the coaxial waveguide tube 64 canpropagate microwaves to the planar antenna member 58.

The planar antenna member 58 is formed of, e.g., a copper plate or analuminum plate whose surface is plated with silver. A multiplicity ofmicrowave irradiation holes 72 each having the shape of, e.g., anelongated through-hole, is formed in the planar antenna member 58. Themicrowave irradiation holes 72 are not particularly limited in theirarrangement pattern but may be arranged, e.g., in a concentric circlepattern, a spiral pattern or a radial pattern.

Further, provided above the mounting table 44 is a gas supply unit 74for supplying a processing gas required in performing a process withinthe processing chamber 42. Specifically, the gas supply unit 74 includesa shower head portion 78 made of, e.g., quartz in which gas a flow pathis formed in a lattice pattern. A multiplicity of gas injection holes 76are formed along the gas flow path.

The mounting table 44 is provided with a plurality of, e.g., three,elevator pins for raising and lowering the semiconductor wafer W duringthe course of loading and unloading the same. The whole part of themounting table 44 is made of a heat-resistant material, e.g., a ceramicmaterial such as alumina or the like.

A thin electrostatic chuck 80 having a conductor wire arranged, e.g., ina net-like pattern, is provided on the upper surface side of themounting table 44. The wafer W placed on the mounting table 44,particularly on the electrostatic chuck 80 is attracted and held inplace by an electrostatic attraction force. The conductor wire of theelectrostatic chuck 80 is connected to a direct current power source 84via a wiring line 82 so that the electrostatic chuck 80 can generate theelectrostatic attraction force. The wiring line 82 is also connected toa radio frequency (RF) bias power supply 86 for applying a RF bias powerof, e.g., 13.56 MHz, to the conductor wire of the electrostatic chuck80.

The gas exhaust port 50 provided in the bottom portion 49 of theprocessing chamber 42 has a circular shape and is formed eccentricallyfrom a center axis 44A vertically extending through the center of themounting table 44. A pressure control valve 88 for controlling thepressure in the processing chamber 42 is directly connected at its gasinlet end to the gas exhaust port 50. A vacuum pump 92 constituting agas exhaust system 90 is directly connected to a gas outlet end of thepressure control valve 88.

More specifically, in case the processing chamber 42 has a size capableof processing a wafer W of 300 mm in size, the diameter of the gasexhaust port 50 is set equal to, e.g., about 200 to 350 mm. The pressurecontrol valve 88 connected to the gas exhaust port 50 is formed of,e.g., a gate valve, and includes a casing 94 of, e.g., a shortcylindrical shape, and a slidingly movable disk-like valve body 96received within the casing 94. The casing 94 has a gas inlet side flange94A air-tightly jointed to the gas exhaust port 50 through a seal member97, such as an O-ring or the like, by means of bolts (not shown). Thecasing 94 is also provided with a gas outlet side flange 94B air-tightlyjointed to the vacuum pump 92 through a seal member 99, such as anO-ring or the like, by means of bolts (not shown).

A circular valve port 98 is formed within the casing 94 in the same sizeas that of the gas exhaust port 50. The valve body 96 is slidinglymovable relative to the valve port 98 in a direction perpendicular tothe flow direction of an exhaust gas. A valve body receiving space 100is formed in one side of the casing 94 so that the valve body 96 can beretracted from the valve port 98.

A seal member 102 formed of an O-ring or the like is provided in a wallthat defines a peripheral portion of the valve port 98. When thepressure control valve 88 is fully closed, the seal member 102 makescontact with the valve body 96 so that the valve port 98 can be closedin a completely air-tight state. An actuator 104 is provided on one sideof the casing 94. The actuator 104 is connected to the valve body 96 byan operating rod (not shown) so that the valve body 96 can be made torectilinearly slide. The actuator 104 is controlled by a valve controlunit 106 including, e.g., a computer. The valve control unit 106 isdesigned to control the valve opening degree of the pressure controlvalve 88, based on the detection values of a pressure detector 108arranged within the processing chamber 42. FIGS. 2A to 2D schematicallydepict the change of the valve opening degree from 0% to 100%.Specifically, FIG. 2A shows a valve opening degree of 0% (a fully closedstate), FIG. 2B shows a valve opening degree of 5%, FIG. 2C shows avalve opening degree of 40%, and FIG. 2D shows a valve opening degree of100% (a fully opened state).

In this regard, it is a feature of the present invention that thepressure control valve 88 is eccentrically arranged to place the centeraxis 44A of the mounting table 44 within an opening region M formed by apractical use region of the valve opening degree of the pressure controlvalve 88. The term “opening region M” used herein refers to the regionof the valve port 98 through which the exhaust gas flows actually (seeFIG. 12). A plan view of the valve port 98 is shown in FIGS. 2A to 2D inwhich the opening region M is indicated by hatching. Therefore, the areaof the opening region M varies with the valve opening degree.

As mentioned earlier, the practical use region of the valve openingdegree refers to a valve opening degree extent over which the targetcontrol pressure, i.e., the process pressure can be regulated with agood controllability in a pressure range around the target controlpressure when the pressure control valve 88 is used in controlling thepressure in the processing chamber 42. In general, the practical userange of the valve opening degree is recommended by control valve makersas a desirable use range. In the illustrated embodiment, the practicaluse region of the valve opening degree is in the range of, e.g., 5 to40%. When processing a wafer, the pressure control valve 88 is usedwithin the extent between the opening region M shown in FIG. 2B whereinthe valve opening degree is 5% and the opening region M shown in FIG. 2Cwherein the valve opening degree is 40%. For this reason, the pressurecontrol valve 88 is attached in an offset state so that the center axis44A of the mounting table 44 can lie within the opening region M shownin FIG. 2C wherein the valve opening degree is 40%.

Referring to FIG. 1, the offset amount (eccentricity amount) is definedby the distance H1 between the center axis 98A of the valve port 98(which coincides with the center axis of the gas exhaust port 50) andthe center axis 44A of the mounting table 44.

Turning to FIGS. 2A to 2D, the symbol “x” stands for the position of thecenter axis 98A of the valve port 98 and the symbol “” denotes theposition of the gravity center G of the plane defined by the openingregion M. In order to more uniformly exhaust the ambient gas in theprocessing space S from around the mounting table 44, it is preferredthat the center axis 44A of the mounting table 44 be positioned on amovement trajectory of the gravity center G of the plane defined by theopening region M.

FIG. 3 illustrates the change in the position of the gravity center G.In this figure, G(5), G(10), G(20) and G(40) indicate the gravitycenters in cases where the valve opening degree is 5%, 10%, 20% and 40%,respectively.

In this way, the gravity center G moves rectilinearly as the valveopening degree is changed. Since the practical use region of the valveopening degree is in the range of 5 to 40%, it is preferable to attachthe pressure control valve 88 such that the center axis 44A of themounting table 44 is positioned on a straight line connecting thegravity centers G(5), G(10), G(20) and G(40). Inasmuch as thefilm-forming and the etching are performed in a valve opening degreerange of 10 to 20% during the actual wafer processing, it is morepreferable to attach the pressure control valve 88 such that the centeraxis 44A of the mounting table 44 is positioned on a straight linejoining the gravity centers G(10) and G(20).

Referring back to FIG. 1, the vacuum pump 92 of the gas exhaust system90 may be, e.g., a turbo molecular pump that can generate a high degreeof vacuum. The gas is exhausted through a gas exhaust pipe 110 connectedto the vacuum pump 92. Although not shown in the drawings, a main vacuumpump operable in a broad band of pressure and a pollution preventingdevice are arranged on the downstream side of the gas exhaust pipe 110.

The overall operation of the plasma processing apparatus 40 iscontrolled by a controller 112 including, e.g., a microcomputer. Thecomputer program for performing this operation is stored in a storagemedium 114 such as a floppy disk, a compact disc (CD), a hard disk drive(HDD), a flash memory or the like. More specifically, the supply andflow rate control of the respective processing gases, the supply andelectric power control of the microwaves and the high-frequency waves,and the control of the process temperature and process pressure areperformed according to commands from the controller 112.

Next, description will be made on a processing method performed by theplasma processing apparatus 40 configured as above.

First, the wafer W is loaded into the processing chamber 42 through thegate valve 48 by a transfer arm (not shown). By vertically moving theelevator pins (not shown), the wafer W is mounted on the upper holdingsurface of the mounting table 44. Then, the wafer W is electrostaticallyattracted and held in place by the electrostatic chuck 80.

If the mounting table 44 is provided with a heating unit, the wafer W isheated by the heating unit to a specified process temperature. Aprocessing gas as required, e.g., an etching gas in case of performingan etching process or a film-forming gas in case of performing a plasmaCVD process, is made to flow at a prescribed flow rate so that theprocessing gas is supplied into the processing chamber 42 from the gassupply unit 74 including the shower head portion 78. At the same time,the vacuum pump 92 of the gas exhaust system 90 is operated and theinterior of the processing chamber 42 is kept at a predetermined processpressure by controlling the pressure control valve 88. Concurrently, themicrowave generator 70 of the plasma generating unit 56 is driven togenerate microwaves which in turn are fed to the planar antenna member58 via the waveguide tube 68 and the coaxial waveguide tube 64. Themicrowaves whose wavelength is shortened by the retardation member 60are introduced into the processing space S, whereby plasma is generatedin the processing space S to perform the etching.

As the microwaves are introduced into the processing chamber 42 from theplanar antenna member 58 in this manner, the processing gas is convertedinto plasma and activated by the microwaves. The surface of the wafer Wis subjected to etching or film-forming by means of the active speciesgenerated at this time. In the plasma processing process, a RF biaspower is applied from the RF bias power supply 86 to the conductor wireof the electrostatic chuck 80, whereby the active species and the likeare drawn to the wafer surface with increased rectilinear mobility.

During the plasma processing process, the ambient gas in the processingchamber 42 is vacuum-exhausted by the vacuum pump 92 of the gas exhaustsystem 90 as set forth above, so that the ambient gas is made to flowdown around the mounting table 44 while diffusing in the processingspace S. Then, the ambient gas passes through the gas exhaust port 50and the opening region M (the hatched region in FIGS. 2A to 2D) of thevalve port 98 of the pressure control valve 88 and flows toward thevacuum pump 92, e.g., the turbo molecular pump. The pressure in theprocessing chamber 42 is detected by the pressure detector 108. Based onthe detected pressure, the valve control unit 106 operates the actuator104 to regulate the opening degree of the valve body 96. Thus, the valvecontrol unit 106 performs feed-back control to maintain a desiredprocess pressure.

In this regard, the process pressure is set to fall within various kindsof pressure ranges depending on the kinds of the processes. Forinstance, the process pressure is set within the range of about 0.5 to 3Pa in case of the plasma etching but is set within the range of about 5to 500 Pa in case of the plasma CVD. In any case, the pressure controlvalve 88 is attached eccentrically from the center axis 44A of themounting table 44 such that the center axis 44A lies within thepractical use region of the valve opening degree, e.g., the openingregion M (the hatched region in FIG. 2C) formed according to the valveopening degree of 5 to 40%, and preferably such that the center axis 44Alies on the movement trajectory of the gravity center joining G(10) andG(20) in FIG. 3. Therefore, the area center of the opening region M isgenerally positioned just below the center portion of the mounting table44 as can be seen in FIG. 4. As a result, the ambient gas in theprocessing space S of the processing chamber 42 is substantiallyuniformly exhausted around the mounting table 44 as indicated by arrows116 in FIG. 4. This ensures that the ambient gas flows down in auniformly distributed state around the mounting table 44. Therefore, itis possible to prevent the gas in the processing space S from flowing ina lopsided or unbalanced state, which would occur in the conventionalapparatus. This makes it possible to process the wafer W with increasedin-plane uniformity.

Now, one example of the actual characteristics of the pressure controlvalve 88 formed as a gate valve will be described with reference toFIGS. 5A and 5B. FIG. 5A represents the relationship between the valveopening degree and the pressure in the processing chamber and FIG. 5Brepresents the relationship between the valve opening degree and anexhaust conductance. In the illustrated example, a nitrogen gas issupplied at a flow rate of 25 sccm and a turbo molecular pump (having acapacity of 800 liters/sec and a minimum exhaust conductance of 5.0liters/sec) is used as the vacuum pump 92.

As represented in FIG. 5A, the change in the pressure in the processingchamber against the change in the valve opening degree is great when thevalve opening degree is in the range of 0 to 20%. This means that thepressure can be relatively easily controlled in this range of valveopening degree. The change in the pressure in the processing chamberagainst the change in the valve opening degree is sharply reduced whenthe valve opening degree is in the range of 20 to 40%. In particular, ifthe valve opening degree exceeds 40%, little change occurs in thepressure in the processing chamber, which means that the pressure comesinto a saturated state. In this range of valve opening degree, it isalmost impossible to control the pressure in the processing chamber. Inaddition, as can be seen in FIG. 5B, the exhaust conductance isexponentially increased together with the increase in the valve openingdegree.

In view of the characteristics represented in FIG. 5A, it can beunderstood that the practical use region of the valve opening degree ofthe pressure control valve is in the range of about 5 to 40% andpreferably in the range of about 10 to 20%. In this case, the valveopening degree recommended by makers of the pressure control valve is inthe range of 5 to 40%.

As described above, with the present invention, the pressure controlvalve 88 is eccentrically provided to ensure that the center axis 44A ofthe mounting table 44 lies within the opening region formed over thepractical use region of the valve opening degree of the pressure controlvalve 88. By arranging the pressure control valve 88 in the gas exhaustport 50 eccentrically from the center axis 44A of the mounting table 44,it is possible to exhaust the ambient gas in the processing space S in auniformly distributed state around the mounting table 44 when thepressure control valve 88 is used in the practical use region of thevalve opening degree. This makes it possible to process the wafer W withincreased in-plane uniformity.

(Modified Example of the Pressure Control Valve)

Next, description will be made on a modified example of the slide-typepressure control valve.

FIG. 6 is a section view showing a modified example of the pressurecontrol valve. FIGS. 7A to 7C are views explaining the change in thevalve opening degree of the pressure control valve shown in FIG. 6. FIG.8 is a plan view illustrating the movement trajectory of the gravitycenter of the plane defined by the opening region when the valve openingdegree is in the range of 5 to 40%. The same components as those shownin FIGS. 1 and 2A to 2D will be designated by like reference numeralsand redundant descriptions thereof will be omitted.

Although the pressure control valve 88 shown in FIGS. 1 and 2A to 2Dincludes the rectilinearly sliding type valve body 96, the valve bodyemployed in this modified example is designed to be swingably slidwithin a so-called horizontal plane along a curvilinear path, e.g., anarc path, like a pendulum. Specifically, as shown in FIGS. 6 and 7A to7C, the pressure control valve 120 of this modified example includes avalve body 96 arranged within a casing 94. An arm 122 extends from oneside of the valve body 96. The arm 122 is fixed at its base end to arotation shaft 104A of an actuator 104. The actuator 104 is attached toa wall defining a valve body receiving space 100 and includes, e.g., arotating motor. As the rotation shaft 104A is reciprocatingly swung, thevalve body 96 is moved curvilinearly to describe an arc in this example.

A magnetic fluid seal 123 for keeping air-tightness is provided in theportion of the casing 94 through which the rotation shaft 104A passes.On the inner wall surface of the casing 94 defining a valve port 98,there is provided an annular seal ring 124 having an “L”-like crosssection. The seal ring 124 is slidable relative to the valve body 96 asindicated by an arrow 126. Seal members 128 and 130 each formed as anO-ring or the like are respectively arranged between the seal ring 124and the inner wall surface of the casing 94 and on the surface of theseal ring 124 that makes contact with the valve body 96. At one end ofthe seal ring 124, there is provided a second actuator 132 including,e.g., an air cylinder. The second actuator 132 is operated by thecommand issuing from the valve control unit 106 (see FIG. 1). When thepressure control valve 120 is fully closed, the second actuator 132presses the seal ring 124 against the valve body 96 to thereby make thevalve opening degree zero. When opening the pressure control valve 120,the seal ring 124 is first moved away from the valve body 96 and thenthe swinging angle of the valve body 96 is controlled according to thevalve opening degree.

FIG. 7A shows the pressure control valve at the valve opening degree of5%, FIG. 7B showing the pressure control valve at the valve openingdegree of 40% and FIG. 7C showing the pressure control valve at thevalve opening degree of 100%. Just like the preceding example, thepressure control valve 120 is eccentrically attached such that thecenter axis 44A of the mounting table 44 lies within the opening regionM available at the valve opening degree of 40% (see FIG. 7B)

In this modified example, the movement trajectory of the gravity centerof the plane defined by the opening region M is of a curvilinear shape,i.e., a generally arcuate shape. Therefore, as illustrated in FIG. 8, itis more preferable to place the center axis 44A of the mounting table 44on the movement trajectory formed between the gravity center G(5)available at the valve opening degree of 5% and the gravity center G(40)available at the valve opening degree of 40%.

Although the vacuum pump 92 of the gas exhaust system 90 is directlyconnected to the pressure control valve 88 in the foregoing embodiment,the present invention is not limited thereto. As in a modified exampleof the attachment structure of the vacuum pump shown in FIG. 9, the gasexhaust pipe 110 of the gas exhaust system 90 may be directly connectedto the pressure control valve 88 and the vacuum pump 92 may be providedon the gas exhaust pipe 110.

Furthermore, although the mounting table 44 is supported by the sidewallof the processing chamber 42 through the “L”-like support arm 46 in theforegoing embodiment, the present invention is not limited thereto. Asin a modified example of the attachment structure of the mounting tableshown in FIG. 10, the mounting table 44 may be supported on the bottomportion 49 of the processing chamber 42 through a plurality of supportlegs 140 having lower portions gradually expanded.

The size and position of the gas exhaust port 50 formed in the bottomportion 49 of the processing chamber 42 does not matter if the gasexhaust port 50 allows the valve port 98 of the pressure control valve88 to be fully led to the interior of the processing chamber 42.

Moreover, although the plasma processing apparatus has been described asan example of the single wafer processing apparatus in the foregoingembodiment, the present invention may be applied to all kinds ofprocessing apparatuses for performing various kinds of processes such asfilm-forming, etching, sputtering, oxidizing and diffusing, reformingand the like regardless of plasma, as long as they are provided with agas exhaust port in a bottom portion of the chamber.

In addition, although the semiconductor wafer has been described as anexample of a target object to be processed in the foregoing embodiment,the present invention is not limited thereto but may be applied to aglass substrate, an LCD substrate, a ceramic substrate and so forth.

1. A processing apparatus for performing a specified process on a targetobject at a predetermined process pressure, the apparatus comprising: anevacuable processing chamber having a gas exhaust port formed in abottom portion thereof; a mounting table provided within the processingchamber for holding the target object; a pressure control valveconnected to the gas exhaust port, the pressure control valve includinga slide-type valve body for changing an area of an opening region of avalve port; and a gas exhaust system connected to the pressure controlvalve, wherein the pressure control valve is eccentrically arranged suchthat a center axis of the mounting table lies within an opening regionof the pressure control valve formed over a practical use region of avalve opening degree of the pressure control valve.
 2. The processingapparatus of claim 1, wherein the gas exhaust port is formedeccentrically relative to the center axis of the mounting table.
 3. Theprocessing apparatus of claim 1, wherein the practical use region of thevalve opening degree is in a range of 5 to 40%.
 4. The processingapparatus of claim 1, wherein the center axis of the mounting table ispositioned on a movement trajectory of a gravity center of a planedefined by the opening region.
 5. The processing apparatus of claim 1,wherein the gas exhaust system includes a turbo molecular pump connectedto the pressure control valve.
 6. The processing apparatus of claim 1,wherein the valve body is rectilinearly slidable.
 7. The processingapparatus of claim 1, wherein the valve body is curvilinearly andswingably slidable.
 8. The processing apparatus of claim 1, wherein themounting table is supported by a sidewall of the processing chamberthrough a support arm.
 9. The processing apparatus of claim 1, whereinthe mounting table is supported on the bottom portion of the processingchamber through support legs.